1. Field of the Invention
The present invention relates to magnetic detecting elements used for hard disk devices and magnetic sensors. In particular, the present invention relates to a magnetic detecting element using an exchange bias method, adapted to the demand for a narrow track width in which the distance between shield layers is reduced while the magnetization of a free magnetic layer is suitably controlled, in which the insulation is ensured between the shield layers and the other layers of the magnetic detecting element, and in which the effective reproduction track width is reduced, and to a method for manufacturing the same.
2. Description of the Related Art
FIG. 20 is a fragmentary sectional view of the structure of a known magnetic detecting element, viewed from a side opposing a recording medium.
The magnetic detecting element includes a lower shield layer 1 formed of a NiFe alloy or the like and a lower gap layer 2 formed of Al2O3 or the like on the lower shielding layer 1.
As shown in FIG. 20, a first antiferromagnetic layer 3, a pinned magnetic layer 4, a nonmagnetic material layer 5, and a free magnetic layer 6 are deposited in that order on the lower gap layer 2. Also, a second antiferromagnetic layer 7 is formed on the upper surface of the free magnetic layer 6 with a space having a predetermined width (=track width Tw) in the track width direction, or the X direction in shown in the drawing, and an electrode layer 8 is formed on the second antiferromagnetic layer 7.
Furthermore, an upper gap layer 9 is formed from the upper surface of the electrode layer 8 to the upper surface of the free magnetic layer 6, and, further, an upper shielding layer 10 is formed on the upper gap layer 9.
The known magnetic detecting element, shown in FIG. 20, has a so-called current-in-plane (CIP) structure in which the electrode layer 8 is disposed on each side of the track width direction (X direction) and, thus, a sense current flows in a direction parallel to the surface of each layer in the multilayer laminate 11 including from the first antiferromagnetic layer 3 to the free magnetic layer 6.
FIG. 21 is a fragmentary sectional view of the structure of anther known magnetic detecting element, viewed from a side opposing a recording medium. This magnetic detecting element has a so-called current-perpendicular-to-plane (CPP) structure in which shield layers 13 and 14, which double as electrodes, are formed on both upper and lower sides of the multilayer laminate 11 in the thickness direction (Z direction in the drawing) and, thus, a sense current flows in each layer of the multilayer laminate 11 in the thickness direction. The shield layer 13 is referred to as a lower shield layer and the shield layer 14 is referred to as an upper shield layer.
In the magnetic detecting element Shown in FIG. 21, an antiferromagnetic layer 7 is covered with an insulating layer 12. The insulating layer 12 prevents the sense current flowing from the upper shield layer 14 to the multilayer laminate 11 from diverging into the second antiferromagnetic layer 7.
Each of the magnetic detecting elements shown in FIGS. 20 and 21 has a so-called exchange bias structure in which the second antiferromagnetic layer 7 is disposed on the free magnetic layer 6 and the magnetization of both ends 6a of the free magnetic layer 6 is fixed in the X direction by the exchange coupling magnetic field generated between the second antiferromagnetic layer 7 and the ends 6a of the free magnetic layer 6, which are in contact with each other.
On the other hand, the central portion 6b of the free magnetic layer 6 is put into a single magnetic domain state in the X direction, by a bias magnetic field generated by exchange interaction in the free magnetic layer 6, and the magnetization changes in response to an external magnetic field.
In the magnetic detecting elements shown in FIGS. 20 and 21, it is desired to reduce the track width in order to adapt them to the demand for high recording density. Accordingly, the track width Tw, which is defined by the width in the x direction of the space in the second antiferromagnetic layer 7, needs to be further reduced.
Unfortunately, the reduction of the track width in the magnetic detecting elements shown in FIGS. 20 and 21 has brought about the following problems.
In the magnetic detecting element shown in FIG. 20, the second antiferromagnetic layer 7 and the electrode layer 8 are disposed on each end portion 6a of the free magnetic layer 6, and the total thickness of these two layers is T1. Therefore, the distance between the lower shield layer 1 and the upper shield layer 10 (hereinafter simply referred to as the distance between the shield layers 1 and 10) is increased to T2 at the end portions 6a of the free magnetic layer 6, while the distance between the shield layers 1 and 10 is T3 at the central portion 6b of the free magnetic layer 6, in which neither the second antiferromagnetic layer 7 nor the electrode layer 8 is formed. Such increase of the distance between the shield layers undesirably increases the actual track width contributing to magnetic reproduction (effective reproduction track width) and the PW50. The PW50 refers to the half-width of the reproduction waveform of a solitary wave.
As described above, although the width of the space in the second antiferromagnetic layers 7 is reduced, the resulting magnetic detecting element cannot be suitably adapted to the demand for a narrow track width in practice because of the increase of the effective reproduction track width and others.
This problem also occurs in the CPP magnetic detecting element shown in FIG. 21, in which the second antiferromagnetic layer 7 is disposed on both end portions 6a of the free magnetic layer 6. Therefore, the distance between the shield layers 13 and 14 is increased to T4 at both end portions 6a of the free magnetic layer 6, while the distance between the shield layers 13 and 14 is T5 at the central portion 6b of the free magnetic layer 6, which does not have the second antiferromagnetic layer 7. Thus, the actual track width contributing to magnetic reproduction, that is, the effective reproduction track width, and the PW50 are undesirably increased.
Also, since, in the known magnetic detecting elements shown in FIG. 20, the second antiferromagnetic layer 7 and the electrode layer 8 are disposed on each end portions 6a of the free magnetic layer 6, it is difficult to ensure that the upper gap layer 9, which is formed from the upper surfaces of the electrode layer 8 to the upper surface of the central portion 6b of the free magnetic layer 6 through the inner side surfaces 7a and 8a of the antiferromagnetic layer 7 and electrode layer 8, has a predetermined thickness particularly on the inner side surfaces 7a and 8a and at the corners 6a1 between the inner side surfaces 7a and 8a and the upper surface of the central portion 6b of the free magnetic layer 6. Consequently, it is difficult to maintain an adequate insulation between the upper shield layer 10 and the electrode layer 8 and between the upper shield layer 10 and the antiferromagnetic layers 7. Also, as thickness T1, which is the total thickness of the antiferromagnetic layer 7 and the electrode layer 8, becomes larger and the inclination of the inner side surfaces 7a and 8a is steeper, it is more difficult to ensure the insulation.
In addition, since the thicknesses of the gap layers 2 and 9 tends to be reduced in order to reduce the gap length between the shield layers 1 and 10, this problem has become more pronounced.
In the CPP magnetic detecting element shown in FIG. 21, since the thickness of the second antiferromagnetic layer 7 is large, it is difficult to form the insulating layer 2 to a predetermined thickness on the inner side surfaces 7a of the second antiferromagnetic layer 7. Consequently, the insulation between the upper shield layer 14 and the second antiferromagnetic layer 7 is not sufficient and, thus, sense current flowing from the upper shield layer 14 to the multilayer laminate 11 diverges into the second antiferromagnetic layer 7. Thus, reproduction output is reduced and side reading occurs disadvantageously.
As one of solutions to overcome the above-described insulation problem, the thickness of the second antiferromagnetic layer 7 may be reduced. However, a reduced thickness of the second antiferromagnetic layer 7 leads to a reduced intensity of the exchange coupling magnetic field generated between the second antiferromagnetic layer and each end portion 6a of the free magnetic layer 6. As a result, since the magnetization of the end portions 6a of the free magnetic layer 6 is not surely fixed, reproduction characteristics are negatively affected, so that off-track characteristics are degraded and linearity is not sufficiently maintained.